Flexible tree

ABSTRACT

Methods, systems and devices for using flexible and efficient partitioning techniques are described. An exemplary method for visual media decoding includes applying, to a current visual media block, a partitioning process that splits the current visual media block into more than four sub-blocks; decoding, based on a bitstream representation, the more than four sub-blocks; and decoding, based on the more than four sub-blocks and the partitioning process, the current visual media block. Another exemplary method for visual media encoding includes receiving input data associated with a current visual media block; applying, to the input data, a partitioning process that splits the current visual media block into more than four sub-blocks; encoding, based on the partitioning process, the more than four sub-blocks; and generating, based on the encoding, a bitstream representation of the current visual media block.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/IB2019/054613, filed on Jun. 4, 2019, which claims the priority to and benefits of International Patent Application No. PCT/CN2018/089918, filed on Jun. 5, 2018. The entire disclosures of the aforementioned applications are incorporated by reference as part of the disclosure of this application in their entireties.

TECHNICAL FIELD

This patent document relates to video coding techniques, devices and systems.

BACKGROUND

In spite of the advances in video compression, digital video still accounts for the largest bandwidth use on the internet and other digital communication networks. As the number of connected user devices capable of receiving and displaying video increases, it is expected that the bandwidth demand for digital video usage will continue to grow.

SUMMARY

This patent document discloses methods, systems, and devices for encoding and decoding digital video by partitioning video pictures using flexible and efficient partitioning techniques.

In one example aspect, a visual media decoding method is disclosed. The method includes applying, to a current visual media block, a partitioning process that splits the current visual media block into more than four sub-blocks; decoding, based on a bitstream representation, the more than four sub-blocks; and decoding, based on the more than four sub-blocks and the partitioning process, the current visual media block.

In another example aspect, a visual media decoding method is disclosed. The method includes receiving input data associated with a current visual media block; applying, to the input data, a partitioning process that splits the current visual media block into more than four sub-blocks; encoding, based on the partitioning process, the more than four sub-blocks; and generating, based on the encoding, a bitstream representation of the current visual media block.

In yet another example aspect, a visual media decoding method is disclosed. The method includes splitting a current visual media block into two or more sub-blocks; applying, to the current visual media block, a partitioning process that splits at least one of the two or more sub-blocks into more than four sub-blocks; decoding, based on a bitstream representation, the more than four sub-blocks; and decoding, based on the more than four sub-blocks and the partitioning process, the current visual media block.

In yet another example aspect, a visual media decoding method is disclosed. The method includes receiving input data associated with a current visual media block; splitting the current visual media block into two or more sub-blocks; applying, to at least one of the two or more sub-blocks, a partitioning process that splits the at least one of the two or more sub-blocks into more than four sub-blocks; encoding, based on the partitioning process, the more than four sub-blocks; and generating, based on the encoding, a bitstream representation of the current visual media block.

In yet another example aspect, a visual media decoding method is disclosed. The method includes applying, to a current visual media block, a partitioning process that splits the current visual media block into more than four sub-blocks; splitting at least one of the more than four sub-blocks into two or more sub-blocks; decoding, based on a bitstream representation, the more than four sub-blocks; and decoding, based on the more than four sub-blocks and the partitioning process, the current visual media block.

In yet another example aspect, a visual media decoding method is disclosed. The method includes receiving input data associated with a current visual media block; applying, to the current visual media block, a partitioning process that splits the current visual media block into more than four sub-blocks; splitting at least one of the more than four sub-blocks into two or more sub-blocks; encoding, based on the partitioning process, the more than four sub-blocks; and generating, based on the encoding, a bitstream representation of the current visual media block.

In yet another example aspect, a visual media encoder device that implements a visual media encoding method described herein is disclosed.

In yet another representative aspect, the various techniques described herein may be embodied as a computer program product stored on a non-transitory computer readable media. The computer program product includes program code for carrying out the methods described herein.

In yet another representative aspect, a visual media decoder apparatus may implement a method as described herein.

The details of one or more implementations are set forth in the accompanying attachments, the drawings, and the description below. Other features will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of a video encoder implementation

FIG. 2 illustrates macroblock partitioning in the H.264 video coding standard.

FIG. 3 illustrates an example of splitting coding blocks (CB) into prediction blocks.

FIG. 4 illustrates an example implementation for subdivision of a CTB into CBs and transform block (TBs). Solid lines indicate CB boundaries and dotted lines indicate TB boundaries, including an example CTB with its partitioning, and a corresponding quadtree.

FIGS. 5A and 5B show an example of a Quad Tree Binary Tree (QTBT) structure for partitioning video data.

FIG. 6 shows examples of (a) quad-tree partitioning, (b) vertical binary-tree partitioning, (c) horizontal binary-tree partitioning, (d) vertical center-side ternary-tree partitioning, and (e) horizontal center-side ternary-tree partitioning.

FIGS. 7A to 7K illustrate examples of partitioning pixel blocks.

FIGS. 8A to 8E shows examples of extended quadtree partitioning.

FIGS. 9A and 9B show example partitions of the largest coding unit of video data.

FIG. 10A is a flowchart showing an example of a method of visual media decoding.

FIG. 10B is a flowchart showing an example of a method of visual media encoding.

FIG. 11 is a block diagram of an example of a hardware platform for implementing a visual media decoding or a visual media encoding technique described in the present document.

DETAILED DESCRIPTION

To improve compression ratio of video, researchers are continually looking for new techniques by which to encode video.

1. Overview of Some Aspects Disclosed in the Present Document

This patent document is related to image/video coding, especially on the partition structure, i.e., how to split one Coding Tree Unit (CTU) into multiple Coding Units (CUs) or how to split one CU into multiple smaller CUs. It may be applied to the existing video coding standard like HEVC, or the standard (Versatile Video Coding) to be finalized. It may be also applicable to future video coding standards or video codec. The techniques described in the present document may be applied for encoding and decoding a video, e.g., a sequence of pictures or images. The techniques may also be used for encoding and decoding of a single picture or an image. Accordingly, the techniques are applicable to encoding or decoding of visual media in the form of video or images. For improved readability, the word “video” is used throughout most of the description to mean video or an image.

2. Discussion

Video coding standards have evolved primarily through the development of the well-known ITU-T and ISO/IEC standards. The ITU-T produced H.261 and H.263, ISO/IEC produced MPEG-1 and MPEG-4 Visual, and the two organizations jointly produced the H.262/MPEG-2 Video and H.264/MPEG-4 Advanced Video Coding (AVC) and H.265/HEVC standards. Since H.262, the video coding standards are based on the hybrid video coding structure wherein temporal prediction plus transform coding are utilized. An example of a typical HEVC encoder framework is depicted shown in FIG. 1 [1].

2.1 Partition Tree Structure in H.264/AVC

The core of the coding layer in previous standards was the macroblock, containing a 16×16 block of luma samples and, in the usual case of 4:2:0 color sampling, two corresponding 8×8 blocks of chroma samples.

An intra-coded block uses spatial prediction to exploit spatial correlation among pixels. Two partitions are defined: 16×16 and 4×4.

An inter-coded block uses temporal prediction, instead of spatial prediction, by estimating motion among pictures. Motion can be estimated independently for either 16×16 macroblock or any of its sub-macroblock partitions: 16×8, 8×16, 8×8, 8×4, 4×8, 4×4 (see FIG. 2) [2]. Only one motion vector (MV) per sub-macroblock partition is allowed.

2.2 Partition Tree Structure in HEVC

In HEVC, a CTU is split into CUs by using a quadtree structure denoted as coding tree to adapt to various local characteristics. The decision whether to code a picture area using inter-picture (temporal) or intra-picture (spatial) prediction is made at the CU level. Each CU can be further split into one, two or four PUs according to the PU splitting type. Inside one PU, the same prediction process is applied and the relevant information is transmitted to the decoder on a PU basis. After obtaining the residual block by applying the prediction process based on the PU splitting type, a CU can be partitioned into transform units (TUs) according to another quadtree structure similar to the coding tree for the CU. One of key feature of the HEVC structure is that it has the multiple partition conceptions including CU, PU, and TU.

In the following, the various features involved in hybrid video coding using HEVC are highlighted as follows.

1) Coding tree units and coding tree block (CTB) structure: The analogous structure in HEVC is the coding tree unit (CTU), which has a size selected by the encoder and can be larger than a traditional macroblock. The CTU consists of a luma CTB and the corresponding chroma CTBs and syntax elements. The size L×L of a luma CTB can be chosen as L=16, 32, or 64 samples, with the larger sizes typically enabling better compression. HEVC then supports a partitioning of the CTBs into smaller blocks using a tree structure and quadtree-like signaling.

2) Coding units (CUs) and coding blocks (CBs): The quadtree syntax of the CTU specifies the size and positions of its luma and chroma CBs. The root of the quadtree is associated with the CTU. Hence, the size of the luma CTB is the largest supported size for a luma CB. The splitting of a CTU into luma and chroma CBs is signaled jointly. One luma CB and ordinarily two chroma CBs, together with associated syntax, form a coding unit (CU). A CTB may contain only one CU or may be split to form multiple CUs, and each CU has an associated partitioning into prediction units (PUs) and a tree of transform units (TUs).

3) Prediction units and prediction blocks (PBs): The decision whether to code a picture area using inter picture or intra picture prediction is made at the CU level. A PU partitioning structure has its root at the CU level. Depending on the basic prediction-type decision, the luma and chroma CBs can then be further split in size and predicted from luma and chroma prediction blocks (PBs). HEVC supports variable PB sizes from 64×64 down to 4×4 samples. FIG. 3 shows examples of allowed PBs for a M×M CU.

4) TUs and transform blocks: The prediction residual is coded using block transforms. A TU tree structure has its root at the CU level. The luma CB residual may be identical to the luma transform block (TB) or may be further split into smaller luma TBs. The same applies to the chroma TBs. Integer basis functions similar to those of a discrete cosine transform (DCT) are defined for the square TB sizes 4×4, 8×8, 16×16, and 32×32. For the 4×4 transform of luma intra picture prediction residuals, an integer transform derived from a form of discrete sine transform (DST) is alternatively specified.

Tree-Structured Partitioning into Transform Blocks and Units

For residual coding, a CB can be recursively partitioned into transform blocks (TBs). The partitioning is signaled by a residual quadtree. Only square CB and TB partitioning is specified, where a block can be recursively split into quadrants, as illustrated in FIG. 4. For a given luma CB of size M×M, a flag signals whether it is split into four blocks of size M/2×M/2. If further splitting is possible, as signaled by a maximum depth of the residual quadtree indicated in the SPS, each quadrant is assigned a flag that indicates whether it is split into four quadrants. The leaf node blocks resulting from the residual quadtree are the transform blocks that are further processed by transform coding. The encoder indicates the maximum and minimum luma TB sizes that it will use. Splitting is implicit when the CB size is larger than the maximum TB size. Not splitting is implicit when splitting would result in a luma TB size smaller than the indicated minimum. The chroma TB size is half the luma TB size in each dimension, except when the luma TB size is 4×4, in which case a single 4×4 chroma TB is used for the region covered by four 4×4 luma TBs. In the case of intrapicture-predicted CUs, the decoded samples of the nearest-neighboring TBs (within or outside the CB) are used as reference data for intrapicture prediction.

In contrast to previous standards, the HEVC design allows a TB to span across multiple PBs for interpicture-predicted CUs to maximize the potential coding efficiency benefits of the quadtree-structured TB partitioning.

2.3 Quadtree Plus Binary Tree (QTBT) Block Structure with Larger CTUs in JEM

To explore the future video coding technologies beyond HEVC, Joint Video Exploration Team (JVET) was founded by VCEG and MPEG jointly in 2015. Since then, many new methods [3] have been adopted by JVET and put into the reference software named Joint Exploration Model (JEM) [4].

2.3.1 QTBT Block Partitioning Structure

Different from HEVC [5], the QTBT structure removes the concepts of multiple partition types, i.e. it removes the separation of the CU, PU and TU concepts, and supports more flexibility for CU partition shapes. In the QTBT block structure, a CU can have either a square or rectangular shape. As shown in FIGS. 5A and 5B, a coding tree unit (CTU) is first partitioned by a quadtree structure. The quadtree leaf nodes are further partitioned by a binary tree structure. There are two splitting types, symmetric horizontal splitting and symmetric vertical splitting, in the binary tree splitting. The binary tree leaf nodes are called coding units (CUs), and that segmentation is used for prediction and transform processing without any further partitioning. This means that the CU, PU and TU have the same block size in the QTBT coding block structure. In the JEM, a CU sometimes consists of coding blocks (CBs) of different colour components, e.g. one CU contains one luma CB and two chroma CBs in the case of P and B slices of the 4:2:0 chroma format and sometimes consists of a CB of a single component, e.g., one CU contains only one luma CB or just two chroma CBs in the case of I slices.

The following parameters are defined for the QTBT partitioning scheme.

-   -   CTU size: the root node size of a quadtree, the same concept as         in HEVC     -   MinQTSize: the minimally allowed quadtree leaf node size     -   MaxBTSize: the maximally allowed binary tree root node size     -   MaxBTDepth: the maximally allowed binary tree depth     -   MinBTSize: the minimally allowed binary tree leaf node size

In one example of the QTBT partitioning structure, the CTU size is set as 128×128 luma samples with two corresponding 64×64 blocks of chroma samples, the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, the MinBTSize (for both width and height) is set as 4×4, and the MaxBTDepth is set as 4. The quadtree partitioning is applied to the CTU first to generate quadtree leaf nodes. The quadtree leaf nodes may have a size from 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If the leaf quadtree node is 128×128, it will not be further split by the binary tree since the size exceeds the MaxBTSize (i.e., 64×64). Otherwise, the leaf quadtree node could be further partitioned by the binary tree. Therefore, the quadtree leaf node is also the root node for the binary tree and it has the binary tree depth as 0. When the binary tree depth reaches MaxBTDepth (i.e., 4), no further splitting is considered. When the binary tree node has width equal to MinBTSize (i.e., 4), no further horizontal splitting is considered. Similarly, when the binary tree node has height equal to MinBTSize, no further vertical splitting is considered. The leaf nodes of the binary tree are further processed by prediction and transform processing without any further partitioning. In the JEM, the maximum CTU size is 256×256 luma samples.

FIG. 5A depicts an example of block partitioning by using QTBT, and FIG. 5B illustrates the corresponding tree representation. The solid lines indicate quadtree splitting and dotted lines indicate binary tree splitting. In each splitting (i.e., non-leaf) node of the binary tree, one flag is signalled to indicate which splitting type (i.e., horizontal or vertical) is used, where 0 indicates horizontal splitting and 1 indicates vertical splitting. For the quadtree splitting, there is no need to indicate the splitting type since quadtree splitting always splits a block both horizontally and vertically to produce 4 sub-blocks with an equal size.

In addition, the QTBT scheme supports the ability for the luma and chroma to have a separate QTBT structure. Currently, for P and B slices, the luma and chroma CTBs in one CTU share the same QTBT structure. However, for I slices, the luma CTB is partitioned into CUs by a QTBT structure, and the chroma CTBs are partitioned into chroma CUs by another QTBT structure. This means that a CU in an I slice consists of a coding block of the luma component or coding blocks of two chroma components, and a CU in a P or B slice consists of coding blocks of all three colour components.

In HEVC, inter prediction for small blocks is restricted to reduce the memory access of motion compensation, such that bi-prediction is not supported for 4×8 and 8×4 blocks, and inter prediction is not supported for 4×4 blocks. In the QTBT of the JEM, these restrictions are removed.

2.4 Ternary Tree for WC

As proposed in [3], tree types other than quad-tree and binary-tree are supported. In the implementation, two more ternary tree (TT) partitions, i.e., horizontal and vertical center-side ternary-trees are introduced, as shown in FIG. 6D and FIG. 6E.

FIGS. 6A-6E show the following examples: (a) quad-tree partitioning, (b) vertical binary-tree partitioning, (c) horizontal binary-tree partitioning, (d) vertical center-side ternary-tree partitioning, and (e) horizontal center-side ternary-tree partitioning, respectively.

In [3], there are two levels of trees, region tree (quad-tree) and prediction tree (binary-tree or ternary-tree). A CTU is firstly partitioned by region tree (RT). A RT leaf may be further split with prediction tree (PT). A PT leaf may also be further split with PT until max PT depth is reached. A PT leaf is the basic coding unit. It is still called CU for convenience. A CU cannot be further split. Prediction and transform are both applied on CU in the same way as JEM. The whole partition structure is named ‘multiple-type-tree’.

3. Drawbacks of Existing Solutions

The prior design of partition trees, such as QTBT or TT have shown much higher coding gains. However, they may also have the following problems:

Both of BT and TT are trying to reduce the number of partitions for a block (either 2 or 3 partitions instead of 4 partitions introduced by QT). For regions with high texture, it may prefer much more partitions (e.g., smaller partitions). With the current design, it may require quite a lot of bits to achieve this.

Instead of modifying the number of partitions, it is also possible that we could modify the quad-tree partitions to cover different cases. The current quad-tree partition always splits one N×N square block into four N/2×N/2 sub-blocks. Introducing more partition patterns may bring additional coding gains.

4. Example Embodiments

Embodiments of the disclosed technology described different partitioning structures, such as extended quad trees (EQT) and flexible trees (FT).

In the following descriptions, it should be noted that only a partition structure is allowed for a certain depth/level, the indication of the usage of such a partition structure may be signaled. In other words, it will automatically skip the signaling of a partition structure if it is disallowed for a certain depth/level. The proposed methods could be applied separately, or combined with each other or combined with existing technologies.

Example 1: An extended quad tree (EQT) partitioning structure is proposed which is corresponding to a block partitioning process including an extended quad tree partitioning process for the block of video data, wherein the extended quad partitioning structure represents partitioning the block of video data into final sub-blocks, and when the extended quad tree partitioning process decides to apply extended quad tree partition to one given block, said one given block is always split into four sub-blocks; decoding the final sub-blocks based on the video bitstream; and decoding the block of video data based on the final sub-blocks decoded according to the EQT structure derived.

Example 1A: The EQT partitioning process can be applied to a given block recursively to generate EQT leaf nodes. Alternatively, when EQT is applied to a certain block, for each of the sub-block due to EQT, it may further be split into BT and/or QT and/or TT and/or EQT and/or other kinds of partition trees.

Example 1B: It is proposed that a block with M×N (M and N are non-zero positive integer values, either equal or unequal) size may be split equally into four partitions, such as M/4×N or M×N/4 (examples are depicted in FIG. 7A and FIG. 7B) or split equally into four partitions and the partition size is dependent on the maximum and minimum values of M and N. In one example, one 4×32 block may be split into four 4×8 sub-blocks while a 32×4 block may be split into four 8×4 sub-blocks.

Example 1C: Alternatively, a block with M×N (M and N are non-zero positive integer values, either equal or unequal) size may be split unequally into four partitions, such as two partitions are with size equal to (M*w0/w)×(N*h0/h) and the other two are with (M*(w−w0)/w)×(N*(h−h0)/h).

For example, w0 and w may be equal to 1 and 2, respectively that is the width is reduced by half while the height could use other ratios instead of 2:1 to get the sub-blocks. Examples for this case are depicted in FIG. 7C and FIG. 7E. Alternatively, h0 and h may be equal to 1 and 2, respectively, that is the height is reduced by half while the width could use other ratios instead of 2:1. Examples for this case are depicted in FIGS. 7D and 7F.

FIG. 7G and FIG. 7H show two alternative examples of extended quad tree partitioning.

FIG. 7I shows a more general case of extended quad tree partitioning with different shapes of partitions wherein each partition may have its own size.

FIG. 7J and FIG. 7K show general examples of FIGS. 7A and 7B wherein the four partitions (c) sub-block width fixed to be M/2, height equal to N/4 or 3N/4, smaller for top two partitions (d) sub-block height fixed to be N/2, width equal to M/4 or 3M/4, smaller for left two partitions may have different sizes, (e) sub-block width fixed to be M/2, height equal to 3N/4 or N/4, smaller for bottom two partitions, (f) sub-block height fixed to be N/2, width equal to 3M/4 or M/4, smaller for right two partitions,

(g) M×N/4 and M/2×N/2; (h) N×M/4 and N/2×M/2,

(i) M1×N1, (M−M1)×N1, M1×(N−N1) and (M−M1)×(N−N1),

(j) M×N1, M×N2, M×N3 and M×N4, where and N1+N2+N3+N4=N, and

(k) M1×N, M2×N, M3×N and M4×N where M1+M2+M3+M4=M.

Example 2: A flexible tree (FT) partitioning structure is proposed which is corresponding to a block partitioning process including an FT partitioning process for the block of video data, wherein the FT partitioning structure represents partitioning the block of video data into final sub-blocks, and when FT partitioning process decides to apply FT partition to one given block, said one given block is split into K sub-blocks wherein K could be larger than 4; decoding the final sub-blocks based on the video bitstream; and decoding the block of video data based on the final sub-blocks decoded according to the FT structure derived.

Example 2A: The FT partitioning process can be applied to a given block recursively to generate FT tree leaf nodes. The partitioning of one node is implicitly terminated when the node reaches a minimally allowed FT leaf node size or FT depth associated with the node reaches a maximally allowed FT depth.

Example 2B: Alternatively, furthermore, the FT depth or the minimally allowed FT leaf node sizes or the minimally allowed partition size for FT may be signaled in sequences parameter set (SPS), and/or picture parameter set (PPS), and/or slice header, and/or CTU, and/or regions, and/or tiles, and/or CUs.

Example 2C: Similar to the proposed EQT, all of the sub-blocks due to FT partitions may be with the same size; alternatively, the sizes of different sub-blocks may be different. Some examples are depicted in FIG. 8A to FIG. 8E with K is equal to 6 or 8 or 16 with equal size of partitions. A block can be split into 16 sub-blocks with equal size in extended quad tree partition, as shown in FIG. 8A to 8E, e.g., an M×N block is split into 16 (M/4)×(N/4) sub-blocks as shown in FIG. 8E. It should be noted that by moving either the horizontal or vertical splitting lines in FIG. 8 may result in other kinds of FT partitions with unequal sizes.

Example 2D: Alternatively, when FT is applied to a certain block, for each of the sub-block due to FT, it may further be split into BT, and/or QT, and/or EQT, and/or TT, and/or other kinds of partition trees.

Example 2D.1 The first level FT is always applied after the first level EQT and/or QT. For example, a LCU is only allowed to split according to one of the EQT and/or QT structures. After that, for partitions of the first level QT/EQT, FT partitioning may be applied. An example of LCU partition is given in FIG. 9A.

Example 2D.2 Alternatively, the first level FT can be applied before all the other kinds of partitions. For example, a LCU is only allowed to split according to one of the FT structure. After that, QT/EQT or other kinds of partitions may be applied. An example of LCU partition is given in FIG. 9B.

Example 2D.3: Alternatively, FT may be put in the same priority as QT and/or EQT. That is, for each LCU, the first level split may be done according to QT and/or EQT and/or FT.

When K is greater than a number K0 and the averaged block size after partitioning is S0, for Cb and Cr components, one bit can be signaled at the parent-node level to indicate whether the cbf of the Cb/Cr blocks are all zero. K0 and S0 can be pre-defined, or individually signaled through either one of the SPS, PPS, VPS, or slice header.

FIGS. 8A to 8E show examples of FT partitions for a M×N block (K=6, or 8, or 16). FIG. 8A shows the example of K=8, M/4×N/2. FIG. 8B shows the example of K=8, M/2×N/4. FIG. 8C shows the example of K=6, M/2×N/2 and M/4×N/2. FIG. 8D shows the example of K=6, M/2×N/2 and M/2×N/4. FIG. 8E shows the example of K=16, M/4×N/4

FIG. 9A shows an example of a LCU is split according to QT firstly (solid line), and for the top-right partition, it is further split according to FT (dotted line).

FIG. 9B shows an example of a LCU is split according to FT firstly (solid line), and for the most top-right partition, it is further split according to EQT (dotted line).

Example 3: The proposed methods may be applied under certain conditions. In other words, when the condition(s) are not satisfied, there is no need to signal the partition types.

Example 3A: Alternatively, the proposed methods may be used to replace the existing partition tree types. Alternatively, furthermore, the proposed methods may be only used as a replacement under certain conditions.

Example 3B: In one example, the condition may include the picture and/or slice types; and/or block sizes; and/or the coded modes; and/or whether one block is located at picture/slice/tile boundary.

Example 3C: In one example, the proposed EQT may be treated in the same way as QT. In this case, when it is indicated that the partition tree type is QT, more flags/indications of the detailed quad-tree partition patterns may be further signaled. Alternatively, EQT may be treated as additional partition patterns.

Example 3D: In one example, the signaling of partitioning methods of EQT or FT or GTT may be conditional, i.e. one or some EQT/FT/GTT partitioning methods may not be used in some cases (e.g., when the corresponding transform matrix for a partition size does not exist), and the bits (or bins) corresponding to signal these partitioning methods are not signaled.

Example 3E: In one example, not all combinations of different EQT, FT, QT or GTT are allowed. In case that one partition structure can be achieved by more than one combinations of EQT, FT, QT and GTT, only one combination is considered as valid and all other combinations are invalid. An example is given as follows, FIG. 8C could also be treated as one M×M block is firstly split into two horizontal BTs and for each BT, vertical TT is further applied. With such an example, if the signaling tells that FT is not utilized for the first depth, BT is used, and for the top BT, vertical TT is applied. When coding the partition structure of the second BT, vertical TT is disallowed, that is, there is no need to signal whether vertical TT is used.

Example 3F: In one example, if the chroma tree follows the same tree as in luma, a partition which results in unavailable chroma partitioning should be disabled for both luma and chroma.

Example 3F1: Alternatively, such partitioning is still allowed for luma, while the associated chroma partitioning is disallowed. In such configuration, both luma and chroma blocks are considered as in the leaf node of a partition tree type.

FIG. 10A is a flowchart representation of a visual media decoding method 1000. The visual media may be a video or a single image. The method 1000 includes, at step 1002, applying, to a current visual media block, a partitioning process that splits the current visual media block into more than four sub-blocks.

The method 1000 includes, at step 1004, decoding, based on a bitstream representation, the more than four sub-blocks.

The method 1000 includes, at step 1006, decoding, based on the more than four sub-blocks and the partitioning process, the current visual media block.

FIG. 10B is a flowchart representation of a visual media encoding method 1020. The visual media may be a video or a single image. The method 1020 includes, at step 1022, receiving input data associated with a current visual media block.

The method 1020 includes, at step 1024, applying, to the input data, a partitioning process that splits the current visual media block into more than four sub-blocks.

The method 1020 includes, at step 1026, encoding, based on the partitioning process, the more than four sub-blocks.

The method 1020 includes, at step 1028, generating, based on the encoding, a bitstream representation of the current visual media block.

In some embodiments, at least one of the more than four sub-blocks is a leaf node.

In some embodiments, the methods 1000 and 1020 further include the step of recursively applying the partitioning process to at least one of the more than four sub-blocks to generate one or more leaf nodes. In an example, recursively applying the partitioning process is implicitly terminated when (i) a size of a leaf node reaches a minimally allowed leaf node size for the partitioning process, or (ii) a depth associated with the at least one of the more than four sub-blocks reaches a maximally allowed depth of the partitioning process. In another example, the minimally allowed leaf node size is signaled in a sequence parameter set (SPS), a picture parameter set (PPS), a slice header, a coding tree unit (CTU), a region, a tile or a coding unit (CU) associated with the current visual media block. In yet another example, the maximally allowed depth is signaled in a sequence parameter set (SPS), a picture parameter set (PPS), a slice header, a CTU, a region, a tile or a CU associated with the current visual media block.

In some embodiments, each of the more than four sub-blocks has a common size.

In some embodiments, a first sub-block of the more than four sub-blocks has a size different from a second sub-block of the more than four sub-blocks.

In some embodiments, a size of the current visual media block is M×N, wherein the more than four sub-blocks comprises L² sub-blocks each with size (M/L)×(N/L), and wherein M, N and L are positive integers.

In some embodiments, the partitioning process further comprises splitting at least one of the more than four sub-blocks using at least one of a binary tree (BT) partitioning process, a quadtree (QT) partitioning process, a ternary tree (TT) partitioning process, or an extended quadtree (EQT) partitioning process.

Embodiments of the disclosed technology provide another method of visual media decoding that includes splitting a current visual media block into two or more sub-blocks; applying, to the current visual media block, a partitioning process that splits at least one of the two or more sub-blocks into more than four sub-blocks; decoding, based on a bitstream representation, the more than four sub-blocks; and decoding, based on the more than four sub-blocks and the partitioning process, the current visual media block.

Embodiments of the disclosed technology provide another method of visual media encoding that includes receiving input data associated with a current visual media block; splitting the current visual media block into two or more sub-blocks; applying, to at least one of the two or more sub-blocks, a partitioning process that splits the at least one of the two or more sub-blocks into more than four sub-blocks; encoding, based on the partitioning process, the more than four sub-blocks; and generating, based on the encoding, a bitstream representation of the current visual media block.

Embodiments of the disclosed technology provide yet another method of visual media decoding that includes applying, to a current visual media block, a partitioning process that splits the current visual media block into more than four sub-blocks; splitting at least one of the more than four sub-blocks into two or more sub-blocks; decoding, based on a bitstream representation, the more than four sub-blocks; and decoding, based on the more than four sub-blocks and the partitioning process, the current visual media block.

Embodiments of the disclosed technology provide yet another method of visual media encoding that includes receiving input data associated with a current visual media block; applying, to the current visual media block, a partitioning process that splits the current visual media block into more than four sub-blocks; splitting at least one of the more than four sub-blocks into two or more sub-blocks; encoding, based on the partitioning process, the more than four sub-blocks; and generating, based on the encoding, a bitstream representation of the current visual media block.

In some embodiments, and in the context of the methods described above, the splitting is based on a quadtree (QT) partitioning process or an extended quadtree (EQT) partitioning process.

In some embodiments, and in the context of any of the methods described above (including, but not limited to methods 1000 and 1020), a number of the four or more blocks is K, wherein K>K0, wherein an average sub-block size for color components of the current visual media block is S0, wherein the bitstream representation comprises one bit that indicates that one or more coded block flags (CBFs) of the color components are all zero, and wherein K, K0 and S0 are positive integers. In an example, K0 and S0 are pre-defined. In another example, K0 or S0 are individually signaled in a sequence parameter set (SPS), a picture parameter set (PPS), a video parameter set (VPS) or a slice header.

In some embodiments, the any of the methods described above further includes the step of making a decision, based on a condition, regarding a selective inclusion of one or more signaling bits for the partitioning process in the bitstream representation.

In an example, the partitioning process replaces an existing partitioning process that includes a binary tree (BT) partitioning process, a ternary tree (TT) partitioning process or a quadtree (QT) partitioning process.

In an example, the condition is based on a picture type or a slice type of a picture or a slice comprising the current visual media block, respectively.

In an example, the condition is based on a size of the current visual media block. In another example, the condition is based on a coding mode of the current visual media block. In yet another example, the condition is based on a location of the current visual media block. In yet another example, the location of the current visual media block is at a boundary of a picture, a slice or a tile comprising the current visual media block.

In an example, the partitioning process is implemented in a similar manner to a quadtree (QT) partitioning process. In another example, the partitioning process is an additional partition pattern to the QT partitioning.

In an example, the condition comprises an unavailability of a transform matrix for a selected partition size of the partitioning process.

In an example, the methods described above further include the step of splitting at least one of more than four sub-blocks using at least one of the partitioning process, an extended quadtree (EQT) partitioning process or a quadtree (QT) partitioning process to generate a final partition structure, wherein only one combination of partitioning processes that result in the final partition structure is valid.

In an example, a chroma component and a luma component of the current visual media block follow a same partition tree, and the condition comprises an exclusion of signaling for both the luma component and the chroma component if a partition of the partitioning process results in an unavailable chroma partitioning.

In an example, a chroma component and a luma component of the current visual media block follow a same partition tree, and the condition comprises an inclusion of signaling for only the luma component when a partition of the partitioning process results in an unavailable chroma partitioning and if both the chroma component and the luma component are leaf nodes of the same partition tree.

In some embodiments, the current visual media block comprises a single image. In other embodiments, the current visual media block comprises a video block.

FIG. 11 shows a block diagram of an example embodiment of a hardware device 1100 that can be utilized to implement various portions of the presently disclosed technology. The hardware device 1100 can be a laptop, a smartphone, a tablet, a camcorder, or other types of devices that are capable of processing videos. The device 1100 includes a processor or controller 1102 to process data, and memory 1104 in communication with the processor 1102 to store and/or buffer data. For example, the processor 1102 can include a central processing unit (CPU) or a microcontroller unit (MCU). In some implementations, the processor 1102 can include a field-programmable gate-array (FPGA). In some implementations, the device 1100 includes or is in communication with a graphics processing unit (GPU), video processing unit (VPU) and/or wireless communications unit for various visual and/or communications data processing functions of the smartphone device. For example, the memory 1104 can include and store processor-executable code, which when executed by the processor 1102, configures the device 1100 to perform various operations, e.g., such as receiving information, commands, and/or data, processing information and data, and transmitting or providing processed information/data to another device, such as an actuator or external display. To support various functions of the device 1100, the memory 1104 can store information and data, such as instructions, software, values, images, and other data processed or referenced by the processor 1102. For example, various types of Random Access Memory (RAM) devices, Read Only Memory (ROM) devices, Flash Memory devices, and other suitable storage media can be used to implement storage functions of the memory 1104. The device 1100 may further include dedicated video processing circuitry 1106 for performing repetitive computational functions such as transforms and decoding. In some embodiments, the video processing circuitry 1106 may be implemented internal to the processor 1102. In some embodiments, the video processing circuitry 1106 may be a graphics processor unit (GPU).

Various possible variations and additions to the methods 1000 and 1020 are described in the examples in Section 2 and the claim section of the present document. For example, a receiving operation may include receiving the bitstream that is locally stored or receiving the bitstream over a network connection (e.g., streaming reception). For example, a deriving operation may be implemented by parsing bits in the video bitstream using a priori knowledge of protocol syntax for the video bitstream. The decoding operations may include generating uncompressed pixel values (luma and or color) from compressed or encoded bit representation of the video.

In some embodiments, a video visual media decoding process may generate decoded video data that may be stored in video buffer and displayed on a user interface for viewing by a user. In some embodiments, a visual media encoding process may be performed on video that is either in uncompressed or lightly compressed format, e.g., captured from a camera device or a digital storage device, and so on.

Improvements achieved by incorporating embodiments of the disclosed technology into HEVC reference software are shown in the experimental results below. The test sequences include HEVC standard test sequences in common test conditions (CTC), which are specified by JCT-VC (Joint Collaborative Team on Video Coding).

Main- Low- Tier Tier Class Sequence RA LDP LDB RA LDP LDB A1 Tango −3.20% −3.19% −3.01% −3.24% −3.84% −3.78% Drums100 −4.21% −4.07% −3.63% −4.80% −5.00% −4.98% CampreParty2 −2.07% −1.89% −1.76% −2.89% −2.96% −2.92% CatRobot −4.07% −4.28% −4.03% −3.92% −5.09% −4.62% A2 TrafficFlow −3.88% −3.78% −3.34% −3.88% −3.20% −3.25% DaylightRoad −4.18% −4.22% −3.98% −3.87% −4.39% −4.06% Kimino −2.36% −2.68% −2.40% −2.51% −3.40% −3.06% ParkScene −3.13% −3.32% −3.05% −3.32% −4.20% −4.02% B Cactus −3.16% −3.12% −3.03% −3.68% −4.09% −4.14% BQTerrace −3.24% −3.24% −2.58% −3.70% −3.49% −3.62% BasketballDrive −3.25% −3.01% −2.63% −3.88% −4.11% −3.78% RaceHorsesC −3.29% −2.58% −2.56% −4.37% −3.79% −3.87% C BQMall −3.50% −3.36% −3.33% −4.22% −5.07% −4.83% PartyScene −2.68% −2.28% −2.47% −3.05% −3.61% −3.59% BasketballDrill −3.22% −2.89% −2.92% −3.95% −3.84% −3.84% RaceHorses −3.17% −2.60% −2.55% −3.92% −3.88% −3.84% D BQSquare −2.16% −2.38% −2.27% −2.34% −2.40% −2.49% BlowingBubbles −2.65% −2.42% −2.71% −2.61% −3.31% −3.44% BasketballPass −2.75% −2.46% −2.39% −3.72% −4.07% −3.90% FourPeople −3.46% −4.18% −4.06% −3.40% −4.64% −4.46% E Jonny −2.94% −4.36% −4.56% −2.86% −3.60% −3.36% KristenAndSara −3.23% −4.15% −4.18% −3.10% −3.76% −4.06% Average −3.17% −3.20% −3.06% −3.51% −3.90% −3.81%

In the above table, the negative percentages indicate bitrate savings for that particular scenario. The various classes (e.g., Class A1, A2, . . . , E) represent different resolutions of the test sequences, the “Main-Tier” and “Low-Tier” designations represent different bitrate ranges, using quantization parameters (QPs) of {22, 27, 32, 37} and {32, 37, 42, 47}, respectively, and “RA”, “LDB” and “LDP” represent different coding conditions.

For example, the resolutions of Classes A1 and A2 are 4K, and the resolutions of Classes B, C, D and E are 1080p, 832×480, 416×240 and 720p, respectively.

For example, “RA” represents random access corresponding to a set of coding conditions designed to enable relatively-frequent random access points in the coded video data, with less emphasis on minimization of delay. In contrast, “LDx” represents low-delay and corresponds to two sets of coding conditions designed to enable interactive real-time communication, with less emphasis on ease of random access. Specifically, “LDB” is a variant of the LD conditions that uses B pictures, and “LDP” is a variant that uses P frames.

From the foregoing, it will be appreciated that specific embodiments of the presently disclosed technology have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Accordingly, the presently disclosed technology is not limited except as by the appended claims.

The disclosed and other embodiments, modules and the functional operations described in this document can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this document and their structural equivalents, or in combinations of one or more of them. The disclosed and other embodiments can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more them. The term “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

The processes and logic flows described in this document can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random-access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

While this document contains many specifics, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in this document should not be understood as requiring such separation in all embodiments.

Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in this document.

5. References

-   [1] “Overview of the High Efficiency Video Coding (HEVC) Standard”,     Gary J. Sullivan, Jens-Rainer Ohm, Woo-Jin Han, and Thomas Wiegand,     IEEE Transactions on Circuits and Systems For Video Technology, Vol.     22, No. 12, December 2012. -   [2] “Overview of the H.264/AVC video coding standard”, Ajay Luthra,     Pankaj Topiwala, Proceedings of SPIE Vol. 5203 Applications of     Digital Image Processing XXVI. -   [3] “Multi-Type-Tree”, JVET-D0117. 

What is claimed is:
 1. A method of visual media processing, comprising: applying, during a conversion between a current visual media block and a bitstream representation of the current visual media block, a partitioning process that splits the current visual media block into more than four sub-blocks at a first depth; splitting at least one of the more than four sub-blocks using at least one of a binary tree (BT) partitioning process, a quadtree (QT) partitioning process, a ternary tree (TT) partitioning process, or an extended quadtree (EQT) partitioning process to generate a final partition structure, wherein only one combination of partitioning processes that result in the final partition structure is valid; and performing the conversion based on the final partition structure.
 2. The method of claim 1, further comprising: recursively applying the partitioning process to at least one of the more than four sub-blocks to generate one or more leaf nodes.
 3. The method of claim 1, wherein the recursively applying the partitioning process is implicitly terminated when (i) a size of a leaf node reaches a minimally allowed leaf node size for the partitioning process, or (ii) a depth associated with the at least one of the more than four sub-blocks reaches a maximally allowed depth of the partitioning process.
 4. The method of claim 1, wherein each of the more than four sub-blocks has a common size.
 5. The method of claim 1, wherein a first sub-block of the more than four sub-blocks has a size different from a second sub-block of the more than four sub-blocks.
 6. The method of claim 1, further comprising: deciding, based on a condition, regarding a selective inclusion of one or more signaling bits for the partitioning process in the bitstream representation.
 7. The method of claim 6, wherein the partitioning process is used to replace an existing partitioning process that includes a binary tree (BT) partitioning process, a ternary tree (TT) partitioning process or a quadtree (QT) partitioning process.
 8. The method of claim 7, wherein the condition is based on a picture type or a slice type of a picture or a slice comprising the current visual media block, respectively.
 9. The method of claim 7, wherein the condition is based on a size of the current visual media block.
 10. The method of claim 7, wherein the condition is based on a coding mode of the current visual media block.
 11. The method of claim 7, wherein the condition is based on a location of the current visual media block, wherein the location of the current visual media block is at a boundary of a picture, a slice or a tile comprising the current visual media block.
 12. The method of claim 7, wherein the partitioning process is treated in the same way as a quadtree (QT) partitioning process.
 13. The method of claim 12, wherein the partitioning process is treated as an additional partition pattern different from the QT partitioning.
 14. The method of claim 7, wherein the condition comprises an unavailability of a transform matrix for a selected partition size of the partitioning process.
 15. The method of claim 1, wherein the conversion includes encoding the current visual media block into the bitstream representation.
 16. The method of claim 1, wherein the conversion includes decoding the current visual media block from the bitstream representation.
 17. An apparatus in a video system comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to: apply, during a conversion between a current visual media block and a bitstream representation of the current visual media block, a partitioning process that splits the current visual media block into more than four sub-blocks at a first depth; split at least one of the more than four sub-blocks using at least one of a binary tree (BT) partitioning process, a quadtree (QT) partitioning process, a ternary tree (TT) partitioning process, or an extended quadtree (EQT) partitioning process to generate a final partition structure, wherein only one combination of partitioning processes that result in the final partition structure is valid; and perform the conversion based on the final partition structure.
 18. The apparatus of claim 17, wherein a first sub-block of the more than four sub-blocks has a size different from a second sub-block of the more than four sub-blocks.
 19. A non-transitory computer readable media storing instructions that cause a processor to: apply, during a conversion between a current visual media block and a bitstream representation of the current visual media block, a partitioning process that splits the current visual media block into more than four sub-blocks at a first depth; split at least one of the more than four sub-blocks using at least one of a binary tree (BT) partitioning process, a quadtree (QT) partitioning process, a ternary tree (TT) partitioning process, or an extended quadtree (EQT) partitioning process to generate a final partition structure, wherein only one combination of partitioning processes that result in the final partition structure is valid; and perform the conversion based on the final partition structure.
 20. A non-transitory computer readable media storing instructions that cause a processor to: apply, during a conversion between a current visual media block and a bitstream representation of the current visual media block, a partitioning process that splits the current visual media block into more than four sub-blocks at a first depth; split at least one of the more than four sub-blocks using at least one of a binary tree (BT) partitioning process, a quadtree (QT) partitioning process, a ternary tree (TT) partitioning process, or an extended quadtree (EQT) partitioning process to generate a final partition structure, wherein only one combination of partitioning processes that result in the final partition structure is valid; and generate the bitstream representation from the current visual media block based on the final partition structure. 